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CONTENTS
Volume 44, Number 3, August10 2022
 

Abstract
The objective of this research is to study experimentally the behavior of stiffened steel tubes (CFSTs). Considered parameters are stiffening methods by through-bolts or shear connectors with different configurations. In addition, the effect of global (ratio between length to diameter) and local (proportion between diameter to thickness) slenderness ratios are investigated. Load application either applied on steel only or both steel and concrete is studied as well. Case of loading on steel only happens when concrete inside the column shrinks. The purpose of the research is to improve the behavior of CFSTs by load transfer between them and different stiffening methods. A parametric experimental study that incorporates thirty-three specimens is carried out to highlight the impact of those parameters. Different outputs are recorded for every specimen such as load capacities, vertical deflections, longitudinal strains, and hoop strains. Two modes of failure occur, yielding and global buckling. Shear connectors and through-bolts improve the ultimate load by up to 5% for sections loaded at steel with different studied global slenderness and local slenderness equal 63.5. Meanwhile, shear connectors or through bolts increase the ultimate load by up to 6% for global slenderness up to 15.75 for sections loaded on composite with local slenderness equals 63.50. Recommendations for future design code development are outlined.

Key Words
composite columns; experimental study, shear connectors, through bolts

Address
Fattouh M.F. Shaker:Department of Structural Engineering, Faculty of Engineering, Helwan University Ain Helwan 11795, Cairo, Egypt

Gouda M. Ghanem:Department of Structural Engineering, Faculty of Engineering, Helwan University Ain Helwan 11795, Cairo, Egypt

Ahmed F. Deifalla:Department of Structural Engineering and construction management, Faculty of Engineering, Future University in Egypt, End of 90th St.,
Fifth Settlement, New Cairo, Cairo 11865, Egypt

Ibrahim S. Hussei:Civil Engineering Program, The Higher Institute of Engineering, El-Shorouk Academy, Nakheel district 11837, Cairo, Egypt

Mona M. Fawzy:Civil Engineering Program, The Higher Institute of Engineering, El-Shorouk Academy, Nakheel district 11837, Cairo, Egypt

Abstract
The post-fire elastic stiffness and performance of concrete-filled steel tube (CFST) columns containing recycled aggregate concrete (RAC) has rarely been addressed, particularly in terms of material properties. This study was conducted with the aim of assessing the modulus of elasticity of recycled aggregate concrete-filled steel tube (RACFST) stub columns following thermal loading. The test data were employed to model and assess the elastic modulus of circular RACFST stub columns subjected to axial loading after exposure to elevated temperatures. The length/diameter ratio of the specimens was less than three to prevent the sensitivity of overall buckling for the stub columns. The gene expression programming (GEP) method was employed for the model development. The GEP model was derived based on a comprehensive experimental database of heated and non-heated RACFST stub columns that have been properly gathered from the open literature. In this study, by using specifications of 149 specimens, the variables were the steel section ratio, applied temperature, yielding strength of steel, compressive strength of plain concrete, and elastic modulus of steel tube and concrete core (RAC). Moreover, parametric and sensitivity analyses were also performed to determine the contribution of different effective parameters to the post-fire elastic modulus. Additionally, comparisons and verification of the effectiveness of the proposed model were made between the values obtained from the GEP model and the formulas proposed by different researchers. Through the analyses and comparisons of the developed model against formulas available in the literature, the acceptable accuracy of the model for predicting the post-fire modulus of elasticity of circular RACFST stub columns was seen.

Key Words
concrete-filled steel tube; elastic modulus; gene expression programming; post-fire behavior; recycled aggregate concrete

Address
Armin Memarzadeh and Amir Ali Shahmansouri:Department of Civil Engineering, University of Mazandaran, Babolsar, Iran

Keerthan Poologanathan:Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, UK

Abstract
In this research, an earthquake-resistant structural system consisting of a pin-connected steel frame and a bracing with metallic fuses is proposed. Contrary to the conventional braced frames, the main structural elements are deemed to remain elastic under earthquakes and the seismic energy is efficiently dissipated by the damper-braces with an amplification mechanism. The superiority of the proposed damping system lies in easy manufacture, high yield capacity and energy dissipation, and an effortless replacement of damaged fuses after earthquake events. Furthermore, the stiffness and the yield capacity are almost decoupled in the proposed damper-brace which makes it highly versatile for performance-based seismic design compared to most other dampers. A special attention is paid to derive the theoretical formulation for nonlinear behavior of the proposed damper-brace, which is verified using analytical results. Next, a direct displacement-based design procedure is provided for the proposed system and an example structure is designed and analyzed thoroughly to check its seismic performance. The results show that the proposed system designed with the provided procedure satisfies the given performance objective and can be used for developing highly efficient low-damage structures.

Key Words
hysteretic dampers; low-damage structures; seismic design; seismic performance; seismic retrofit; steel bracing

Address
Mohammad Mahdi Javidan and Jinkoo Kim:Department of Global Smart City, Sungkyunkwan University, Suwon, Republic of Korea

Abstract
A mortar-filled rectangular hollow structural section (RHS) can increase a structural section property as well as a compressive buckling capacity of a RHS member. In this study, the tensile performance of newly developed mortar-filled RHS members was experimentally evaluated with various connection details. The major test parameters were the type of end connections, the thickness of cap plates and shear plates, the use of stud bolts, and penetrating bars. The test results showed that the welded T-end connection experienced a brittle weld fracture at the welded connection, whereas the tensile performance of the T-end connection was improved by additional stud bolts inserted into the mortar within the RHS tube. For the end connection using shear plates and penetrating stud bolts, ductile behavior of the RHS tube was achieved after yielding. The penetrating bars increased load carrying capacity of the RHS. Based on the analysis of the load transfer mechanism, the current design code and test results were compared to evaluate the tensile capacity of the RHS tube according to the connection details. Design considerations for the connections of the mortar-filled RHS tubes were also recommended.

Key Words
end-plate connection; mortar-filled tube (MFT); penetrating rebar; rectangular hollow section (RHS); shear end plate; spatial structures; steel truss; stud bolt connection; tensile test; welded T-end connection

Address
Chul-Goo Kim:Department of Architectural and Urban Systems Engineering, Ewha Womans University, Seoul, 03760, Republic of Korea

Su-Min Kang:School of Architecture, Soongsil University, Seoul, 06978, Republic of Korea

Tae-Sung Eom:Department of Architectural Engineering, Dankook University, Gyeonggi, 16891, Republic of Korea

Jang-Woon Baek:Department of Architectural Engineering, Kyung Hee University, Gyeonggi, 17104, Republic of Korea

Abstract
This study attempts to shed light on the coupled impact of types of loading, thickness stretching, and types of variation of Winkler–Pasternak foundations on the flexural behavior of simply- supported FG plates according to the new quasi– 3D high order shear deformation theory, including integral terms. A new function sheep is used in the present work. In particular, both Winkler and Pasternak layers are non-uniform and vary along the plate length direction. In addition, the interaction between the loading type and the variation of Winkler–Pasternak foundation parameters is considered and involved in the governing equilibrium equations. Using the virtual displacement principle and Navier's solution technique, the numerical results of nondimensional stresses and displacements are computed. Finally, the non-dimensional formulas' results are validated with the existing literature, and excellent agreement is detected between the results. More importantly, several complementary parametric studies with the effect of various geometric and material factors are examined. The present analytical model is suitable for investigating the bending of simply-supported FGM plates for special technical engineering applications.

Key Words
FGM plates; Navier'technique; non-uniform Winkler–Pasternak foundations; original quasi–3D theory; several types of load

Address
Nabil Himeur:1)Reactive Materials and Systems Laboratory (LMSR), Department of mechanical Engineering, University of Sidi Bel Abbes, Faculty of
Technology, Algeria 2)Department of mechanical Engineering, University of Abbés Laghrour Khenchela, Faculty of Science and Technology, Algeria

Belgacem Mamen:3)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
4)Department of Civil Engineering, University of Abbès Laghrour Khenchela, Faculty of Science and Technology, Algeria

Soumia Benguediab:Department of Civil Engineering and Hydraulic, University of Saida, Algeria

Abdelhakim Bouhadra:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
2)Department of Civil Engineering, University of Abbès Laghrour Khenchela, Faculty of Science and Technology, Algeria

Abderrahmane Menasria:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
2)Department of Civil Engineering, University of Abbès Laghrour Khenchela, Faculty of Science and Technology, Algeria

Benattou Bouchouicha:Reactive Materials and Systems Laboratory (LMSR), Department of mechanical Engineering, University of Sidi Bel Abbes, Faculty of
Technology, Algeria

Fouad Bourada:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
2)Department of Civil Engineering and Hydraulic, University of Saida, Algeria

Mohamed Benguedia:Reactive Materials and Systems Laboratory (LMSR), Department of mechanical Engineering, University of Sidi Bel Abbes, Faculty of
Technology, Algeria

Abdelouahed Tounsi:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria 2)YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea 3) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,
Eastern Province, Saudi Arabia


Abstract
The present study tackles the problem of forced vibration of imperfect axially functionally graded shell structure with truncated conical geometry. The linear and nonlinear large-deflection of the structure are considered in the mathematical formulation using von-Kármán models. Modified coupled stress method and principle of minimum virtual work are employed in the modeling to obtain the final governing equations. In addition, formulations of classical elasticity theory are also presented. Different functions, including the linear, convex, and exponential cross-section shapes, are considered in the grading material modeling along the thickness direction. The grading properties of the material are a direct result of the porosity change in the thickness direction. Vibration responses of the structure are calculated using the semi-analytical method of a couple of homotopy perturbation methods (HPM) and the generalized differential quadrature method (GDQM). Contradicting effects of small-scale, porosity, and volume fraction parameters on the nonlinear amplitude, frequency ratio, dynamic deflection, resonance frequency, and natural frequency are observed for shell structure under various boundary conditions.

Key Words
functionally graded material; forced nonlinear vibration; homotopy perturbation; micro-structures; semianalytical solution

Address
Peng Zhang:Faculty of Architecture and Civil Engineering, Huaiyin Institute of Technology, Huaian, 223001, China

Yanan Gao:Faculty of Architecture and Civil Engineering, Huaiyin Institute of Technology, Huaian, 223001, China

Zohre Moradi:Faculty of Engineering and Technology, Department of Electrical Engineering, Imam Khomeini International University, 34149-16818 Qazvin, Iran

Yasar Ameer Ali:Building and Construction Techniques Engineering Department, Al-Mustaqbal University College, Babylon, Iraq

Mohamed Amine Khadimallah:1)Prince Sattam Bin Abdulaziz University, College of Engineering, Civil Engineering Department, Al-Kharj, 16273, Saudi Arabia
2)Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia

Abstract
Recycling concrete construction waste is an encouraging step toward green and sustainable building. A lot of research has been done on recycled aggregate concretes (𝑅𝐴𝐶s), but not nearly as much has been done on concrete made with recycled aggregate. Recycled aggregate concrete, on the other hand, has been found to have a lower mechanical productivity compared to conventional one. Accurately estimating the mechanical behavior of the concrete samples is a most important scientific topic in civil, structural, and construction engineering. This may prevent the need for excess time and effort and lead to economic considerations because experimental studies are often time-consuming, costly, and troublous. This study presents a comprehensive data-mining-based model for predicting the splitting tensile strength of recycled aggregate concrete modified with glass fiber and silica fume. For this purpose, first, 168 splitting tensile strength tests under different conditions have been performed in the laboratory, then based on the different conditions of each experiment, some variables are considered as input parameters to predict the splitting tensile strength. Then, three hybrid models as GWO-RF, GWO-MLP, and GWO-SVR, were utilized for this purpose. The results showed that all developed GWO-based hybrid predicting models have good agreement with measured experimental results. Significantly, the GWO-RF model has the best accuracy based on the model performance assessment criteria for training and testing data.

Key Words
hybrid prediction algorithms; glass fiber; recycled aggregate concrete; silica-fume; splitting tensile strength

Address
Yirong Zhu:1)School of Management Engineering, Zhejiang Guangsha Vocational and Technical University of Construction, Dongyang, 322100, China
2)Glodon Company Limited, Beijing, 100193, China

Lihua Huang:School of Management Engineering, Zhejiang Guangsha Vocational and Technical University of Construction, Dongyang, 322100, China

Zhijun Zhang:Southwest China Architectural Design and Research Institute Corp. Ltd, Chengdu 610042, China

Behzad Bayrami:Department of Civil Engineering, Moghadas Ardabili Institute of Higher Education, Ardabil, Iran

Abstract
Prefabricated hybrid wind turbine towers (WTTs) are promising due to height increase. This study proposes the use of ultra-high performance concrete (UHPC) to develop a new type of WTT without the need to use reinforcement. It is demonstrated that the UHPC WTT structure without reinforcing bars could achieve performance similar to that of reinforced concrete WTTs. To simplify the design of WTT, a design approach for the calculation of stresses at the horizontal joints of a WTT is proposed. The stress distribution near the region of the horizontal joint of the WTT structure under normal operating conditions and different load actions is studied using the proposed approach, which is validated by the finite element method. A further parametric study shows that the degree of prestressing and the bending moment both significantly affect the principal stress. The shear-to-torsion ratio also shows a significant influence on the principal tensile stress.

Key Words
design; finite element; hybrid; post-tensioned; precast concrete; stress; UHPC; wind turbine towers

Address
Xiangguo Wu:1)College of Civil Engineering, Fuzhou University, Fuzhou 350108, China
2)Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Key Lab of Smart Prevention and Mitigation of Civil
Engineering Disasters of the Ministry of the Industry and Information Technology, Harbin Institute of Technology, Harbin 150090, China

Xuesen Zhang:CGN New Holdings Co., Ltd, Beijing 100070, China

Qingtan Zhang:Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Key Lab of Smart Prevention and Mitigation of Civil
Engineering Disasters of the Ministry of the Industry and Information Technology, Harbin Institute of Technology, Harbin 150090, China

Dong Zhang:College of Civil Engineering, Fuzhou University, Fuzhou 350108, China

Xiaojing Yang:College of Civil Engineering, Fuzhou University, Fuzhou 350108, China

Faqiang Qiu:JianYan Test Group Co., Ltd, Xiamen, Fujian 361004, China

Suhyun Park:Department of Architecture & Architectural Engineering, Seoul National Univ., Seoul 08826, Korea

Thomas H.-K. Kang:Department of Architecture & Architectural Engineering, Seoul National Univ., Seoul 08826, Korea

Abstract
This paper proposes an innovative thin-walled square concrete filled steel tubular (CFST) column with an octagonal/circular lining steel tube, in which the outer steel tube and the inner liner are fabricated independently of each other and connected by slot-weld or self-tapping screw connections. Twelve thin-walled square CFST columns were tested under quasi-static loading, considering the parameters of liner type, connection type between the square tube and liner, yield strength of steel tube, and the axial load ratio. The seismic performance of the thin-walled square CFST columns is effectively improved by the octagonal and circular liners, and all the liner-stiffened specimens showed an excellent ductile behavior with the ultimate draft ratios being much larger than 1/50 and the ductility coefficients being generally higher than 4.0. The energy dissipation abilities of the specimens with circular liners and self-tapping screw connections were superior to those with octagonal liner and slot-weld connections. Based on the test results, both the finite element (FE) and simplified theoretical models were established, considering the post-buckling strength of the thin-walled square steel tube and the confinement effect of the liners, and the proposed models well predicted the hysteretic behavior of the liner-stiffened specimens.

Key Words
confinement effect; hysteretic numerical model; octagonal/circular liner tube stiffener; seismic behavior; thin-walled square CFST

Address
Xuanding Wang:School of Civil Engineering, Chongqing University, Chongqing 400045, China

Jiepeng Liu:School of Civil Engineering, Chongqing University, Chongqing 400045, China

Xian-Tie Wang:School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China

Guozhong Cheng:School of Civil Engineering, Chongqing University, Chongqing 400045, China

Yan Ding:School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China

Abstract
When the vertical load-bearing members in high-rise structures fail locally, the beam-column joints play an important role in the redistribution of the internal forces. In this paper, a static laboratory test of three full-scale flush flange beam-reinforced connections with side and cover plates (CP-FBSP connection) with double half-span steel beams and single Lshaped columns composed of concrete-filled steel tubes (L-CFST columns) was conducted. The influence of the side plate width and cover plate thickness on the progressive collapse resistance of the substructure was thoroughly analyzed. The failure mode, vertical force-displacement curves, strain variation, reaction force of the pin support and development of internal force in the section with the assumed plastic hinge were discussed. Then, through the verified finite element model, the corresponding analyses of the thickness and length of the side plates, the connecting length between the steel beam flange and cover plate, and the vertical-force eccentricity were carried out. The results show that the failure of all the specimens occurred through the cracking of the beam flange or the cover plate, and the beam chord rotations measured by the test were all greater than 0.085 rad. Increasing the length, thickness and width of the side plates slightly reduced the progressive collapse resistance of the substructures. The vertical-force eccentricity along the beam length reduced the progressive collapse resistance of the substructure. An increase in the connecting length between the beam flange and cover plate can significantly improve the progressive collapse resistance of substructures.

Key Words
flush flange beam-reinforced connection; L-CFST column; progressive collapse; static test; FE analysis

Address
Qingqing Xiong:1)Key Laboratory of Roads and Railway Engineering Safety Control
(Shijiazhuang Tiedao University), Ministry of Education, Hebei Province, China
2)School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, Hebei Province, China
3)Department of Civil Engineering, Tianjin University, Tianjin, China

Wenbo Wu:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, Hebei Province, China

Wang Zhang:1)Key Laboratory of Roads and Railway Engineering Safety Control
(Shijiazhuang Tiedao University), Ministry of Education, Hebei Province, China
2)School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, Hebei Province, China
3)Department of Civil Engineering, Tianjin University, Tianjin, China

Zhihua Chen:Department of Civil Engineering, Tianjin University, Tianjin, China

Hongbo Liu:Dali Construction Group Corporation Limited, Hangzhou, Hebei Province, China


Tiancheng Su:

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